Numerous metabolic disorders, such as hyperammonemia and aminoacidopathies, are characterized by a chronic elevation of a specific metabolite due to dysfunction of enzymes involved in metabolic regulation, process and clearance. These high levels of metabolites can be biochemically evaluated by measuring plasma levels using well defined analytical methods and result in specific tissue toxicity, which define the symptomatology of each disease. It would be of great utility and convenience to develop sensors able to detect specific plasma metabolites in real-time in similar fashion of what, for example, has been done with glucose and diabetes. Point of care sensors would allow doing immediate blood level evaluation of specific metabolites, facilitating the management, treatment and follow up of metabolic disorders. Recent estimations of the prevalence of metabolic and endocrine disorders in USA reveal that at least 5% of the population suffers from an endocrine disorder and more than 47 million of US residents have a metabolic syndrome. Besides the tremendous human suffering and the high impact on the health care costs, the management of these diseases is difficult and expensive not only in terms of medications, analytical monitoring, and follow-up of patients, but in many cases results in unnecessary procedures and hospitalizations. Although important advances have been made in specific disorders such as diabetes or hypercholesterolemia, advances in others with lower prevalence have been delayed. For example, not much advance has been made in obtaining new diagnostic or therapeutic solutions for patients with Hyperammonemia and Aminoacidopathies. Currently the monitoring of metabolite levels has to be done in a hospital equipped with a specialized mass spectrometry instrumentation, and therefore every time that these patients have an appearance of a crisis, whether related or unrelated to the elevation of the corresponding metabolite, they need to visit the hospital in order for the specialized testing to be performed. It would thus be extremely advantageous, from both a patient quality-of-life and a financial management standpoint, to develop devices capable of detecting and quantifying these metabolites in real time.